Gaius Suetonius Tranquillus, commonly referred to as Suetonius, was a Roman historian who wrote during the early Imperial era of the Roman Empire. His most important surviving work is a set of biographies of 12 successive Roman rulers from Julius Caesar to Domitian, properly titled De vita Caesarum. Other works by Suetonius concerned the daily life of Rome, politics, oratory, and the lives of famous writers, including poets, historians, and grammarians. A few of these books have partially survived, but many have been lost.

The history of the Roman Empire covers the history of ancient Rome from the fall of the Roman Republic in 27 BC until the abdication of Romulus Augustulus in AD 476 in the West, and the Fall of Constantinople in the East in AD 1453. Ancient Rome became a territorial empire while still a republic, but was then ruled by Roman emperors beginning with Augustus, becoming the Roman Empire following the death of the last republican dictator, the first emperor's adoptive father Julius Caesar.